Plasma polymerization has been widely employed for coating various types of targets, primarily due to the uniformity of deposits on the target. To meet design standards for ablatively driven targets capable of imploding gases to high densities, the coating thickness must be uniform within 2 percent of the wall thickness, void free, and smooth with few defects.
Plasma polymerization of various gaseous groups utilizes a gas discharge to dissociate gas molecules into ions and free radicals. The molecular fragments later recombine to form a brittle polymer coating. Previous investigators have employed inductively coupled discharge devices operating at about 36 MHz to form either fluorocarbon or hydrocarbon coatings.
Boron hydride polymers have lower molecular weights than hydrocarbon polymers and hence should show significantly better ablation performance. Attempts to produce boron hydride polymers have been reported previously. These methods failed to produce a smooth surface polymer which is desirable for various applications. Such methods include the thermopyrolysis of volatile borons, electric discharge, photolysis with ultraviolet light, electrolysis discharge, CO.sub.2 laser arc ablation of B.sub.2 H.sub.6 sensitized with SF.sub.6, and shock tube adiabatic compression.
Although hydrocarbons have been employed as coatings for substrates including microballoons, boron hydride polymers have a higher ablation pressure and hence are more desirable. Accordingly, it would be an advancement to provide boron hydride polymers which possess smooth surface areas (no defect on the surface higher than about 0.1 micrometer) which can be coated on a suitable substrate such as a target microballoon.